What is frictional heat?

All of you can generate frictional heat easly.
Please rub your both hands. Then they will become hotter and hotter. This is frictional heat.
Nowadays, eco carzs generate energy with frictional heats which ,when we brake applied, generated by tires and ground recriminated.
Frictional heats are used in many fields.
For example,the disappearing ball-point,Friction Ball.Its ink color changes by heat. The heat is generated with frictional heat. Frictional heat which is generated between ball-point's rubber at tip and a paper changes ink color.